Urea resin foam has been used for various applications and recently its utilization for rice-seedling raising mats is increasing. For this purpose good water absorption is especially required. Since the introduction of rice planting machines has effectively mechanized transplantation of paddy rice and reduced the labor, this way of transplantation is increasingly adopted year by year, accounting for half of the total cultivation area of paddy rice in Japan, i.e. about a half of 2.7 million ha, in 1975.
In order to secure paddy rice seedling to be used for mechanized transplantation, an enormous amount of soil is needed. Moreover, various adjustments are required for such soil to be used for raising seedling, and considerable time and labor are spent. For this reason, artificial cultivation soil which can be easily handed without any adjustment tends to be increasingly employed year by year.
Artificial cultivation soil which is light and very easily applicable requires the following properties:
(1) good water absorption PA1 (2) good water retention PA1 (3) easy intrusion of plant roots PA1 (4) pH of the soil ranging from 4 to 7 PA1 (5) soil easily crushed with rake of the rice planting machine
Urea resin foam has already properties (2), (3) and (5), and its pH can be easily adjusted to within the range of 4.about.7. However, providing water absorption has been a most important problem to be solved, because high water repellency is a property inherent to urea resin foam.